The present invention relates to a fuel cell system, a controller thereof and a method, and more particularly, to a fuel cell system, a controller thereof and a method for controlling demand power during acceleration in response to a charge level of a battery.
Since a fuel cell system of the type wherein feed material is reformed to produce hydrogen gas necessary for electric power generation relatively has a low response characteristic in production of electric power during a transient condition, a battery of a large capacity is required in order to compensate for variation in demand power.
In a start-up control of such a fuel cell system, it is a usual practice to monitor a charge level of the battery and to vary the flow rate of feed material to be reformed in the combustor in response to the charge level of the battery. In particular, a control process is employed wherein when the charge level of the battery is low, a fuel cell is started in operation to charge the battery. With such a control process, in order to meet rapid-rate variations in demand power needed for acceleration, a vehicle must carry a battery of a large size at high cost.
In view of the investigation by the present inventor, on the contrary, in order to meet demand power varying at the rapid rate, with the use of a battery of a small size, it has heretofore been thought to immediately infer a driver""s will for acceleration from an accelerator pedal""s depressed position or a throttle opening and to implement control such that when acceleration at the rapid rate is discriminated, demand power, which is resultantly to be produced by the fuel cell, is increased and when rapid acceleration is discriminated, the demand power is corrected to a further increased level.
In such a fuel cell system, however, since demand power is corrected to an increased level dominantly by a displacement value of the accelerator pedal or degree of the throttle valve, i.e., rapid-rate acceleration and slow-rate acceleration, accelerating at a low charge level of a battery causes a shortage in output power, probably resulting in poor accelerating performance.
Further, in order to augment the poor accelerating performance caused by shortage of power output, although it has been contemplated to control so as to increase the amount of demand power regardless of the battery charge level, the flow rate of hydrogen gas to be supplied to the fuel cell will increase beyond a higher level than necessary, with a resultant increase in the amount of surplus hydrogen gas owing to less consumption in hydrogen gas by the fuel cell. Then owing to combustion of the surplus hydrogen gas, the temperature of the combustor is increased to an excessively high level, causing undesirable effects therein.
It is therefore an object of the present invention to overcome the above situations investigated by the present inventor and to provide a fuel cell system, controller thereof and method for controlling demand power in response to a battery charge level during acceleration.
In the present invention, a fuel cell system is provided with: a fuel cell producing output power; a battery discharging output power; a battery charge level monitoring unit monitoring and detecting a charge level of the battery; an accelerator""s displacement sensor detecting an accelerator""s displacement value; and a controller calculating demand power to be produced by the fuel cell based on the accelerator""s displacement value detected by the accelerator""s displacement sensor, calculating an accelerator""s displacement value per unit time based on the accelerator""s displacement value, and correcting the demand power based on the accelerator""s displacement value per unit time and the charge level of the battery detected by the battery charge level monitoring unit.
In other words, a controller of a fuel cell system having a fuel cell producing output power and a battery discharging output power is provided with: means for monitoring and detecting a charge level of the battery; means for detecting an accelerator""s displacement value; means for calculating demand power to be produced by the fuel cell based on the accelerator""s displacement value; means for calculating an accelerator""s displacement value per unit time based on the accelerator""s displacement value; and means for correcting the demand power based on the accelerator""s displacement value per unit time and the charge level of the battery.
Besides, a method of controlling a fuel cell system, which has a fuel cell producing output power and a battery discharging output power, monitoring and detecting a charge level of the battery; detecting an accelerator""s displacement value; calculating demand power to be produced by the fuel cell based on the accelerator""s displacement value; calculating an accelerator""s displacement value per unit time based on the accelerator""s displacement value; and correcting the demand power based on the accelerator""s displacement value per unit time and the charge level of the battery.
Other and further features, advantages, and benefits of the present invention will become more apparent from the following description taken in conjunction with the following drawings.